If you've decided to dress as a scary, creepy character this Halloween, you're likely to have plenty of company. Witches, zombies, ghouls, vampires, and werewolves are perennial favorites of young and old alike.

You should also know, however, that most of these characters have medical and psychological "baggage," say the handful of experts who study them.

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So don't just take along a vial of blood or some magic potion to make your character more believable. Find out the possible medical and psychological reasons that may have made them so frightening in the first place. But beware: Even the experts disagree on the truth surrounding some of the creepiest Halloween characters.

Halloween Character Case File No. 1: Witches

Witches got a mostly bad rap as sinister types who cast spells in the Middle Ages, says Stanley Krippner, PhD, professor of psychology at the Saybrook Graduate School in San Francisco. And it's typically undeserved, he insists. They may be the most psychologically healthy of all the creepy Halloween characters. "In the Middle Ages, some of the witches were probably emotionally disturbed," he tells WebMD. "But in my opinion, most of them were not. They were very good herbalists and midwives. Some of them were surgeons.

"Remember, this was an era where women didn't have much power," Krippner says of the witches' heyday in the Middle Ages. "This was one way they could get some respect."

Some witches, he suspects, were better doctors than the men doing the healing back in those days. But as the witches got more powerful, buying up land wanted by the men, he says the anti-witch crusades occurred, including the witch hunts of the 14th century.

Not all the witches back in the Middle Ages were on that level, of course, Krippner says. "As with any profession, there probably were a few kooks."

Halloween Character Case File No. 2: Zombies

Zombies could be considered innocent bystanders, just the guy or gal next door -- until someone in the villages of yore decided they had done something wrong. "They then would go to a trial by ordeal," says James D. Adams, PhD, associate professor of pharmacology and pharmaceutical sciences at the University of Southern California School of Pharmacy, Los Angeles, and an expert in zombie history.